Question

I’d like to learn how to better write a more generic method which can be called onload and onclick. This is what I have thus far which works perfectly.

rushJustification($("#rush"));

$("input#rush").click(function() {
    rushJustification($(this));
});

function rushJustification(obj) {
    var rushInput = obj.is(':checked');
    var rushContainer = $("#rush-justification-container");

    if(rushInput) {
       rushContainer.slideDown(300);
    } else {
       rushContainer.hide();
    }
}

Answer 1

Instead of copying the contents of the click handler, trigger it as well:

$("input#rush").click(function() {
    rushJustification($(this));
}).click();

The previously mentioned method can have some side effects, when other scripts have already bound an event. In your case, you can then use the following code:

rushJustification( $("input#rush").click(function() {
    rushJustification($(this));
}) );

It may look weird at first. This feature is possible, because of jQuery’s chainability. The click method returns the same jQuery collection, namely $('input#rush'). This is then passed as an argument to the rushJustification function.